The present invention is directed to color measurement and, more particularly, to a method for establishing accuracy and consistency in the measurement of color measuring instruments located at a number of facilities.
Color measuring instruments are widely employed to determine whether the color of various articles being produced meets the specifications for the desired color of that product. Sometimes different manufacturers, and/or different locations of the same manufacturer, may be producing parts which are intended to have the same color so that they will match when assembled. Moreover, replacement parts should also have the same color as the originally produced parts.
If all production were to be measured by the same color measuring instrument, and assuming that the color measuring instrument were properly maintained and serviced, there would be no significant problem in ensuring that the measurement results are consistent for that instrument since it can be periodically checked using a set of color standards.
However, when production is taking place at a multiplicity of locations employing different instruments and even instruments of different manufacturers, consistency in measurements from instrument to instrument is unlikely, and, in fact, it is likely that there will be substantial deviation in the results which would be obtained from measurement of the same part on the different instruments. Unfortunately, there is even variation between sets of color standards used to measure the performance or calibrate the instruments. Some color measuring instruments tend to exhibit drift in the measurements which they will generate over a period of time. Obviously, if a manufacturer cannot be assured that all of the parts it is making which are intended to have the same color values can be tested to determine that they do so, there would be a need to match parts of the same color coming from different sources.
Accordingly, it is an object of the present invention to provide a novel method for establishing management control over a series of color measuring instruments at remote locations to ensure that the measurements obtained by use of different instruments are accurate and related.
It is also an object to provide such a method in which the individual facilities making parts can certify to the customer that the parts produced meet the color specifications established for the part.
Another object is to provide such a method in which a master color lab can maintain supervisory control over the measurement techniques and instruments being employed at a multiplicity of locations and provide corrective action.
It has now been found that the foregoing and related objects may be readily attained in a method for maintaining substantial reliability of color measurements generated by a number of color measuring instruments and thereby confirming the substantial uniformity of color of products produced at several facilities. Color values of a set of master color standards are measured on a master color measuring instrument at a master color lab, and thereafter color values of sets of working color standards are measured on the master color measuring instrument to determine calibration values based upon the deviations in values determined for the working set from the values determined for the set of master color standards. The sets of working color standards are provided to remote locations for use on remote color measuring instruments. The remote locations measure the sets of working color standards to obtain color value measurements which are transmitted to the master color lab.
The master color lab compares the measurements from the remote color measuring instruments with the calibration values obtained from measurements on the master color measuring instrument for that respective set of working color standards to generate remote instrument measurement profiles reflecting the variations in measurements attributable to each of the remote color measuring instruments. These remote instrument measurement profiles are provided to the remote color labs which measure color values for their sets of working color standards and apply the remote instrument measurement profiles to the measured color values to provide corrected color values which are transmitted to the master color lab. The corrected color values are analyzed to determine compliance with specifications as to permissible deviations.
In operation, the remote color measuring instruments are used to measure color values of articles to determine compliance with color specifications for the articles and to certify those articles which comply with the color specifications as being within the color specifications.
Periodically, the sets of working standards are remeasured on the remote measurement instruments and the remeasured color values are transmitted to the master color lab which analyzes the remeasured color values to determine that the instruments are in compliance with specifications as to permissible deviations. Desirably, the steps of comparing and analyzing are performed by computers, and the transmitting steps are performed by electronic transmission. The periodic remeasurement and analysis steps are performed at regular intervals.
In this manner, remote color measurement instruments located at a multiplicity of remote locations communicate with a computer at the master color lab, and the several steps are performed with respect to each of the remote measurement instruments to provide uniform color testing at the multiplicity of locations.